Cement compositions may be used in a variety of subterranean applications. For example, in subterranean well construction, a pipe string (e.g., casing, liners, expandable tubulars, etc.) may be run into a well bore and cemented in place. The process of cementing the pipe string in place is commonly referred to as “primary cementing.” In a typical primary cementing method, a cement composition may be pumped into an annulus between the walls of the well bore and the exterior surface of the pipe string disposed therein. The cement composition may set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement (i.e., a cement sheath) that may support and position the pipe string in the well bore and may bond the exterior surface of the pipe string to the subterranean formation. Among other things, the cement sheath surrounding the pipe string functions to prevent the migration of fluids in the annulus, as well as protecting the pipe string from corrosion. Cement compositions also may be used in remedial cementing methods, for example, to seal cracks or holes in pipe strings or cement sheaths, to seal highly permeable formation zones or fractures, to place a cement plug, and the like. Cement compositions also may be used in surface applications, for example, construction cementing.
Cement compositions utilized in subterranean operations may be lightweight to prevent excessive hydrostatic pressure from being exerted on subterranean formations penetrated by the well bore, whereby the formations may be unintentionally fractured. One type of lightweight cement composition is a foamed cement composition, i.e., a cement composition that comprises entrained gas. In addition to being lightweight, the gas contained in the foamed cement composition may improve the ability of the composition to maintain pressure and prevent the flow of formation fluids into and through the cement composition during its transition time, i.e., the time during which the cement composition changes from a true fluid to a set mass. Foamed cement compositions may also be advantageous because they have low fluid loss properties and may act to prevent the loss of fluid circulation. Additionally, foamed cement compositions when set have a lower modulus of elasticity than non-foamed cements, which is often desirable as it enables the resultant set cement, for example, to resist hoop stresses exerted on the set cement in the annulus.
A foamed cement composition generally may be prepared by mixing a gas, such as air or nitrogen, with the cement composition. Foamed cement composition typically further may comprise a variety of surfactants commonly referred to as “foaming surfactants” for facilitating the foaming of a cement composition and various other surfactants commonly referred to as “foam stabilizers” for preventing the components of the foamed cement composition from prematurely separating. While a variety of foaming agents and foam stabilizers are well known in the art, problems have been associated with their use. For example, certain foaming agents, such as those consisting of a surfactant of Formula 1, R—(OR′)n—OSO3—X+, and foam stabilizers, such as a glycol of Formula 2, CH3O—(CH2CH2O)nH, or a betaine surfactant, may lower the compressive strength of the resultant set cement composition. Furthermore, upon mixing, the foaming agents and foam stabilizers used heretofore with water, gelation may occur, which is undesirable. Moreover, some foaming agents and/or foam stabilizers may have undesirable environmental characteristics and/or may be limited by strict environmental regulations in certain areas of the world.